Apparatus and method of driving backlight unit and display apparatus employing the same

ABSTRACT

An apparatus and a method of driving a backlight unit and a display apparatus employing the same. Wherein a driving current, which is divided in a step-by-step fashion, is sequentially changed and output according to a current control signal. The current control signal is divided into low levels and high levels that are consecutively and repeatedly applied to a backlight controller. The driving current is reduced from a reference current corresponding to a number of the high levels during a time period that starts when the low level is applied for at least a first reference time interval and ends when the high level is applied for at least a second reference time interval.

CROSS-REFERENCE TO RELATED APPLICATION

This application relies for priority upon Korean Patent Application No.2008-29887 filed on Mar. 31, 2008, the contents of which are hereinincorporated by reference in their entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to an apparatus and a method of driving abacklight unit and a display apparatus employing the same.

2. Discussion of Related Art

A display apparatus to display information has occupied an importantposition in modern society. Accordingly, recently, various displayapparatuses have been developed and extensively used in various fields.

Among such display apparatuses, a flat panel display has been mainlyused for electronic appliances. As a representative flat panel display,a liquid crystal display (LCD) displays images using electrical andoptical characteristics of liquid crystal. Because the LCD has a slimand light structure and operates at low power consumption and a lowdriving voltage as compared with other display apparatuses, the LCD hasbeen widely used overall in many industrial fields.

The LCD includes a liquid crystal panel to display an image, a backlightunit to supply light to the liquid crystal display panel, and a driverto drive the liquid crystal display panel and the backlight unit.

In a conventional LCD, an adaptive brightness control (ABC) scheme hasbeen employed in a dimming process in order to reduce power consumptionof the backlight unit. According to the ABC scheme, a current of thebacklight unit is automatically adjusted according to the brightness ofexternal light and the brightness of a displayed image. When the ABCscheme is performed through pulse code modulation (PCM), even though thePCM has advantages in terms of less noise of a driving current andoperational stability of the LCD, a person recognizes the brightnessvariation of a screen when the LCD is abruptly driven in a darkenvironment, so that the person does not sufficiently conceive the imagebeing displayed.

SUMMARY

Therefore, an exemplary embodiment of the present invention provides anapparatus driving a backlight unit capable of adaptively controllingbrightness according to an external condition without any deteriorationof image quality.

An exemplary embodiment of the present invention provides a method ofdriving the backlight unit.

An exemplary embodiment of the present invention provides a displayapparatus employing the driving apparatus and method.

In an exemplary embodiment of the present invention, a method of drivinga backlight unit is performed as follows. A driving current, which isdivided step by step, is selectively changed and output according to acurrent control signal. The current control signal is divided into lowlevels and high levels that are consecutively and repeatedly applied.The driving current is reduced from a reference current corresponding toa number of the high levels during a time period that starts when thelow level is applied for at least a first reference time interval andends when the high level is applied for at least a second reference timeinterval.

The low level is applied for less than a third reference time interval.The driving current may not be output when the low level is applied forat least the third reference time interval.

The driving current may be reduced by one step whenever the high levelis applied after the low level is applied for less than the firstreference time interval.

In an exemplary embodiment of the present invention, a method of drivinga backlight unit is performed as follows.

A first driving current reduced by a predetermined level is output whena first clock is applied. A second driving current reduced by n timesthe predetermined level, is output when a second clock having a perioddifferent from a period of the first clock is applied, in which the n isa natural number greater than or equal to 2.

The second clock may be applied when a low level of the first clock isapplied for at least a first reference time interval and for less than asecond reference time interval.

The second driving current may be output when a high level of the secondclock is applied for at least a third reference time interval.

The n is a number of high levels of the second clock when the highlevels of the second clock are applied for less than the third referencetime interval.

The second driving current is reduced step by step and then reduced to apredetermined level.

In an exemplary embodiment of the present invention, an apparatus ofdriving a backlight unit includes a modulator and a backlightcontroller. The modulator consecutively and repeatedly applies lowlevels and high levels of a current control signal. The backlightcontroller reduces a driving current, which is divided step by step,from a reference current according to the current control signal, andoutputs the driving current to a backlight unit. The modulator appliesthe high levels for at least a second reference time interval after thelow levels are applied for at least a first reference time interval,such that the driving current is reduced from the reference currentcorresponding to a number of the high levels.

The modulator may apply the low levels for less than a third referencetime interval.

The modulator may apply the low levels for at least the third referencetime interval to turn off the backlight unit.

The modulator may apply the low levels for less than the first referencetime interval and then apply the high levels to reduce the drivingcurrent step by step.

In an exemplary embodiment of the present invention, a display apparatusincludes a display panel, a backlight unit, a backlight controller, anda modulator. The display panel displays an image. The backlight unitsupplies light to the display panel. The backlight controller supplies adriving current, which is gradually divided, to the backlight unit byreducing the driving current from a reference current according to acurrent control signal. The modulator consecutively and repeatedlyapplies low levels and high levels of the current control signal to thebacklight controller. The modulator applies the high levels for at leasta second reference time interval after the low levels are applied for atleast a first reference time interval, such that the driving current isreduced from the reference current corresponding to a number of theapplied high levels.

The backlight unit includes a light emitting diode.

The modulator may apply the low levels for less than a third referencetime interval.

The modulator may apply the low levels for at least the third referencetime interval to turn off the backlight unit.

The modulator may apply the low levels for less than the first referencetime interval and then the high levels to reduce the driving current ina step-by-step fashion.

The display panel further includes a sensor to measure brightness of asurrounding environment.

The modulator may modulate an image of the display panel and informationabout the brightness of the surrounding environment into the currentcontrol signal.

According to above, the driving current is selectively changed accordingto the brightness of a display image and the brightness of a surroundingenvironment and applied to a backlight unit, thereby reducing powerconsumption of the backlight unit.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention will be understood inmore detail from the following descriptions taken in conjunction withthe accompanying drawings wherein:

FIG. 1 is a block diagram showing an exemplary embodiment of a displayapparatus according to the present invention;

FIG. 2 is a flowchart showing an exemplary embodiment of a method ofdriving a backlight unit according to an exemplary embodiment of thepresent invention;

FIG. 3 is a timing chart showing the variation of a backlight drivingcurrent according to the present invention; and

FIG. 4 is a timing chart showing the variation of a backlight drivingcurrent according to a current control signal in order to explain themethod of driving the backlight unit shown in FIG. 2.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, an apparatus and a method of driving a backlight unit and adisplay apparatus employing the same according to an exemplaryembodiment of the present invention will be described in detail withreference to the accompanying drawings, so that those of ordinary skillin the art can completely understand the present invention. The size oflayers and regions shown in the drawings can be simplified or magnifiedfor the purpose of clear explanation. In addition, the same referencenumerals are used to designate the same elements throughout thedrawings.

FIG. 1 is a block diagram showing an exemplary embodiment of a displayapparatus according to the present invention.

Referring to FIG. 1, the display apparatus includes a display panel 100,a timing controller 160, a power supply 170, a gate driver 180, a datadriver 190, a modulator 200, a backlight unit 220, and a backlightcontroller 210.

The display panel 100 includes a plurality of gate lines GL1 to GLm anda plurality of data lines DL1 to DLn that cross the gate lines GL1 toGLm, a thin film transistor 111, and a liquid crystal capacitor Clcconnected to the thin film transistor 111. The display panel 100 furtherincludes a sensor 150 to detect the brightness of the surroundingenvironment. The sensor 150 provides external optical information to themodulator 200 as a photo-voltage VPO in order to measure the brightnessof the surrounding environment.

The timing controller 160 converts external data signals EDATA inputfrom an external device into data signals DATA, which can be processedby the data driver 190, and supplies the data signals DATA to the datadriver 190. The timing controller 160 generates a data control signalDCS to control the data driver 190 and a gate control signal GCS tocontrol the gate driver 180 and applies the data and gate controlsignals DCS and GCS to the data driver 190 and the gate driver 180,respectively. The data control signal DCS generated from the timingcontroller 160 includes a source start pulse and a source clock. Thegate control signal GCS includes a gate start pulse and a gate shiftclock.

The power supply 170 converts input power VIN supplied from an externaldevice into power required for the gate driver 180 and the data driver190 and then applies the power to the gate driver 180 and the datadriver 190. More specifically, the power supply 170 converts the inputpower VIN to apply a gate-on-voltage VON and a gate-off-voltage VOFF tothe gate driver 180 and to apply a gamma voltage VGMA to the data driver190.

The gate driver 180 receives the gate control signal GCS from the timingcontroller 160, and the gate-on-voltage VON and the gate-off-voltageVOFF from the power supply 170. The gate driver 180 sequentially appliesthe gate-on-voltage VON to the gate lines GL1 to GLm. The gate driver180 applies a gate-off-voltage VOFF to the gate line GL to which thegate-on-voltage VON is applied. In other words, the gate driver 180simultaneously turns on a plurality of thin film transistors 111sequentially connected to the gate lines GL1 to GLm.

The data driver 190 receives the data control signal DCS and the datasignals DATA from the timing controller 160, and receives the gammavoltage VGMA used to express the gray scale of the data signals DATAfrom the power supply 170 and applies the data signals DATA and thegamma voltage VGMA to the data lines DL1 to DLn.

The modulator 200 converts the photo-voltage VPO input from the sensor150 into first digital data. The modulator 200 analyzes imageinformation IMAGE input from the timing controller 160 to convert thebrightness of pixel data into second digital data. Then, the modulator200 mixes the first and second digital data into third digital data. Inthis case, the modulator 200 mixes the first and second digital datathrough an algorithm capable of controlling the brightness of thebacklight unit 220. The modulator 200 modulates the third digital datainto a current control signal LCS having low and high levels and appliesthe current control signal LCS to the backlight controller 210 tocontrol the light output of the backlight unit 220. The modulator 200can modulate the current control signal LCS through a pulse codemodulation (PCM) scheme or through pulse width modulation (PWM).

The modulator 200 may consecutively and repeatedly apply low levels andhigh levels of the current control signal LCS to the backlightcontroller 210. In this exemplary embodiment, the modulator 200 mayapply the low levels for at least a first reference time interval andthen the high levels for at least a second reference time interval, suchthat a backlight driving current ILED is reduced corresponding to thenumber of the applied high levels. In addition, the modulator 200 mayapply the high levels after applying the low levels for less than thefirst reference time such that the backlight driving current ILED isgradually reduced.

The backlight unit 220 includes a light emitting diode, hereinafter,referred to as “an LED”, to generate light and supplies the light to thedisplay panel 100. The LED is a current driven element, and receives thebacklight driving current ILED from the backlight controller 210 inorder to drive the backlight unit 220.

The backlight controller 210 converts the backlight voltage VLEDreceived from the power supply 170 into the backlight driving currentILED. The backlight controller 210 applies the backlight driving currentILED to the backlight unit 220. The backlight controller 210 applies thebacklight driving current ILED, which is divided step by step, to thebacklight 220 according to the current control signal LCS applied fromthe modulator 200.

Hereinafter, a method of driving the backlight unit 220 according to anexemplary embodiment of the present invention will be described withreference to FIGS. 2 to 4. FIG. 2 is a flowchart showing an exemplaryembodiment of the method of driving the backlight unit 220 according tothe present invention, and FIG. 3 is a timing chart showing thevariation of the backlight driving current ILED according to the presentinvention. FIG. 4 is a timing chart showing the variation of thebacklight driving current ILED according to the current control signalLCS in order to explain the method shown in FIG. 2 for driving thebacklight unit 220 shown in FIG. 1.

Referring to FIGS. 2 to 4, in the method of driving the backlight unit220, the backlight driving current ILED, which is divided in astep-by-step fashion, is selectively changed and provided according tothe current control signal LCS.

The backlight driving current ILED is applied to the backlight unit 220to turn on the backlight unit 220 (S11). As shown in FIG. 3, themodulator 200 applies an initial high level HCLK of the current controlsignal LCS to the backlight controller 210 for at least a reference timeinterval D1 of the lighting period. The backlight controller 210 outputsthe backlight driving current ILED having the maximum intensity N whenthe initial high level HCLK is applied for more than the reference timeinterval D1 of the lighting period. For example, as shown in FIG. 3, theintensity of the backlight driving current ILED may be divided step bystep from the maximum intensity N to the minimum intensity 0.1N.

Then, the modulator 200 applies a low level LCLK of the current controlsignal LCS to the backlight controller 210 (S21). After outputting thebacklight driving current ILED having the maximum intensity N, themodulator 200 applies the low level LCLK to the backlight controller 210for a predetermined time interval. At this time, the backlightcontroller 210 determines whether the low level LCLK is applied for atleast the first reference time interval or not (S23). If the low levelLCLK is applied for at least the first reference time interval, thebacklight controller 210 determines whether the low level LCLK isapplied for less than the second reference time interval or not (S25).

As shown in FIG. 4, if the low level LCLK is applied for at least afirst reference time interval T4 and for less than a second referencetime interval T1, the backlight controller 210 shown in FIG. 1recognizes a present mode as a preliminary mode P2. In other words, thesecond reference time interval T1 is longer than the first referencetime interval T4. In addition, the backlight controller 210 recognizesthe present mode as a sequential mode P1 if the low level LCLK isapplied for less than the first reference time interval T4. Thebacklight controller 210 recognizes the present mode as an off-mode P4if the low level LCLK is applied for at least the second reference timeinterval T1.

Then, the modulator 200 applies the high level HCLK to the backlightcontroller 210 in the preliminary mode P2 and the sequential mode P1.

In the preliminary mode P2, the backlight controller 210 determineswhether the high level HCLK is applied for a third reference timeinterval T2 or not (S33). As shown in FIG. 4, if the high level HCLK isapplied for less than the third reference time interval T2 in thepreliminary mode P2, the backlight driving current ILED having uniformintensity is output. After the high level HCLK is applied for less thanthe third reference time interval T2, the modulator 200 consecutivelyapplies the low level LCLK and the high level HCLK (S41 and S31).

Then, if the high level HCLK is applied for at least the third referencetime interval T3 in the preliminary mode P2, the backlight controller210 recognizes the present mode as a jump mode P3, and checks the numberof the high levels HCLK applied for less than the third reference timeinterval T3 (S51). As shown in FIG. 4, the backlight controller 210recognizes two high levels HCLK applied for less than the thirdreference time interval T3.

Next, the backlight controller 210 shown in FIG. 1 changes the intensityof the backlight driving current ILED corresponding to the number of theapplied high levels HCLK based on a reference current intensity (S61).The reference current intensity refers to the intensity of the backlightdriving current ILED output in the preliminary mode P2.

Then, the backlight controller 210 outputs the backlight driving currentILED that is changed corresponding to the number of the applied highlevels HCLK (S71). As shown in FIG. 4, the backlight controller 210outputs the backlight driving current ILED having the intensity of 0.6Nchanged from the reference current intensity of 0.8N corresponding totwo steps.

In this exemplary embodiment, in the sequential mode P1 in which the lowlevel LCLK is applied for less than the first reference time intervalT4, the backlight controller 210 changes the intensity of the backlightdriving current ILED by one step from a reference current intensity whenthe high level HCLK is applied (S101). For example, as shown in FIG. 3,the reference current intensity is the maximum current intensity of N.

Next, the backlight controller 210 outputs the backlight driving currentILED having the current intensity 0.9N changed from the referencecurrent intensity N corresponding to one step (S11).

Finally, in the off-mode P4, the backlight controller 210 outputs thebacklight driving current ILED having an off current intensity at a timepoint at which the low level LCLK is applied for at least the secondreference time interval D2, so that the backlight unit 220 is turned off(S81).

Meanwhile, the backlight controller 210 may receive clocks havingdifferent periods in the sequential mode P1 and the preliminary mode P2.The clock is the current control signal LCS. For example, the clockapplied in the sequential mode P1 has a period covering the low levelLCKL applied for less than the first reference time interval T4. Theclock applied in the preliminary mode P2 has a period covering the lowlevel LCLK applied for at least the first reference time interval T4 andfor less than the second reference time interval T1 and the high levelHCLK applied for less than the third reference time interval T2.

According to the above-described exemplary embodiment, a driving currentis selectively changed according to the brightness of the display imageand the brightness of the surrounding environment and is applied to thebacklight unit, thereby reducing power consumption of the backlightunit.

Further, the driving apparatus for the backlight unit may change thebrightness of the backlight unit adaptively for a surroundingenvironment as compared with a conventional apparatus employing aconventional PCM scheme. In addition, the driving apparatus for thebacklight unit may apply a constant driving current and prevent noise ofthe control signal, so that the apparatus may be stably operated, ascompared with conventional apparatus employing the conventional PWMscheme.

Although the exemplary embodiments of the present invention have beendescribed, it is understood that the present invention should not belimited to these exemplary embodiments but various changes andmodifications can be made by one of ordinary skill in the art within thespirit and scope of the present invention as hereinafter claimed.

1. A method of driving a backlight unit, the method comprising:selectively changing and outputting a driving current, which is dividedin a step-by-step fashion, according to a current control signal,wherein the current control signal includes low levels and high levelsthat are consecutively and repeatedly applied, and wherein the drivingcurrent is reduced in one step from a reference current by the number ofhigh levels during a time period that starts when a low level of the lowlevels is applied for at least a first reference time interval and endswhen a high level of the high levels is applied for at least a secondreference time interval.
 2. The method of claim 1, wherein a low levelof the low levels is applied for less than a third reference timeinterval.
 3. The method of claim 2, wherein an output of the drivingcurrent stops when a low level of the low levels is applied for at leastthe third reference time interval.
 4. The method of claim 1, wherein thedriving current is reduced by one step whenever a high level of the highlevels is applied after a low level of the low levels is applied forless than the first reference time interval.
 5. A method of driving abacklight unit, the method comprising: outputting a first drivingcurrent reduced stepwise by a predetermined level whenever a first clocksignal is applied; and outputting a second driving current reduced inone step by n times the predetermined level, when a second clock signalhaving a period different from a period of the first clock signal isapplied, wherein n is a natural number greater than or equal to
 2. 6.The method of claim 5, wherein the second clock signal is applied when alow level of the first clock signal is applied for at least a firstreference time interval and for less than a second reference timeinterval.
 7. The method of claim 6, wherein the second driving currentis output when a high level of the second clock signal is applied for atleast a third reference time interval.
 8. The method of claim 7, whereinn is the number of high levels of the second clock signal before thehigh level of the second clock signal is applied for at least the thirdreference time interval.
 9. The method of claim 8, wherein the seconddriving current is reduced in a step-by-step fashion and then reduced toa predetermined level.
 10. An apparatus for driving a backlight unit,the apparatus comprising: a backlight controller; and a modulator thatconsecutively and repeatedly applies low levels and high levels of acurrent control signal to the backlight controller, wherein thebacklight controller reduces a driving current, which is divided in astep-by-step fashion, from a reference current according to the currentcontrol signal, and outputs the driving current to a backlight unit, andwherein the modulator applies a high level of the high levels for atleast a second reference time interval after a low level of the lowlevels is applied for at least a first reference time interval, suchthat the driving current is reduced in one step from the referencecurrent by the number of high levels between the first reference timeinterval and the second reference time interval.
 11. The apparatus ofclaim 10, wherein the modulator applies a low level of the low levelsfor less than a third reference time interval.
 12. The apparatus ofclaim 11, wherein the modulator applies a low level of the low levelsfor at least the third reference time interval to turn off the backlightunit.
 13. The apparatus of claim 12, wherein the modulator applies a lowlevel of the low levels for less than the first reference time intervaland then applies the high levels to reduce the driving current in astep-by-step fashion.
 14. A display apparatus comprising: a displaypanel that displays an image; a backlight unit that supplies light tothe display panel; a backlight controller that supplies a drivingcurrent, which is gradually divided, to the backlight unit by reducingthe driving current from a reference current according to a currentcontrol signal; and a modulator that consecutively and repeatedlyapplies low levels and high levels of the current control signal to thebacklight controller, and applies a high level of the high levels for atleast a second reference time interval after a low level of the lowlevels is applied for at least a first reference time interval, suchthat the driving current is reduced in one step from the referencecurrent by the number of high levels between the first reference timeinterval and the second reference time interval.
 15. The displayapparatus of claim 14, wherein the backlight unit comprises a lightemitting diode.
 16. The display apparatus of claim 15, wherein themodulator applies a low level of the low levels for less than a thirdreference time interval.
 17. The display apparatus of claim 16, whereinthe modulator applies a low level of the low levels for at least thethird reference time interval to turn off the backlight unit.
 18. Thedisplay apparatus of claim 15, wherein the modulator applies a low levelof the low levels for less than the first reference time interval andthen applies the high levels to reduce the driving current in astep-by-step fashion.
 19. The display apparatus of claim 14, wherein thedisplay panel further comprises a sensor to measure brightness of asurrounding environment.
 20. The display apparatus of claim 19, whereinthe modulator modulates an image of the display panel and informationabout the brightness of the surrounding environment into the currentcontrol signal.